A vascular stent is a medical device used in a blood vessel to expand the blood vessel when the blood vessel becomes narrow due to various diseases occurring in a human body and thus blood circulation disorder, and the like, occurs. Therefore, a raw material constituting the stent should have particularly high biocompatibility with a human body and stability in addition to mechanical properties such as flexibility, and the like, for insertion in a complicated and curved blood vessel at the time of an operation.
However, when a predetermined time elapses after a stent operation, restenosis frequently occurs due to accumulation of blood clots and fat inside the stent. Recently, as a method for suppressing restenosis, a drug-eluting stent (DES) coated with a small amount of a drug capable of suppressing cell growth to thereby continuously release the drug was developed. Representative examples of the drug-eluting stent include a paclitaxel-eluting stent (TAXUS™), a sirolimus-eluting stent (Cypher™), everolimus-eluting stent, (XIENCE PRIME, Abbott) (here, sirolimus and everolimus are immunosuppressants), and the like. However, there were still problems to be solved such as inflammation due to use of a polymer, late thrombosis, and the like.
A technology of manufacturing a drug-eluting stent may be classified depending on a method of loading a drug on a stent. For example, there are a method of directly attaching the drug to a metal stent, a method of loading the drug in pores of a porous metal stent, a method of binding the drug to a polymer coated on the stent, and the like, and currently, various researches into the methods have been conducted.
The method of binding the drug to the polymer coated on the stent has an advantage in that since the drug is bound to the polymer, release of the drug is delayed and thus, restenosis may be suppressed or delayed, but the method causes a local acidic environment due to a polymer decomposition or swelling phenomenon generated in a drug elution process by various enzymes in blood vessels, solvents, and the like. This causes other side effects such as late thrombosis, suppression of re-endothelialization, and the like.
Recently, various researches into the drug-eluting stent using everolimus, which is a drug suppressing proliferation and having an excellent immunosuppressive effect to thereby be mainly used to manufacture the drug-eluting stent, have been conducted.
However, there are still various technical difficulties in a stent capable of inducing sustained release of a drug by stably maintaining binding of everolimus without deterioration of chemical stability of everolimus and a technology of manufacturing the stent.